There are two statements of the second law. The process, and (5) correlate physical properties. So we see two, although appearing to be different, actually can be that the second law is quite valuable. shown to be equivalent. Therefore, we state only one of them, the Kelvin-Planck version: I.2.4 Efficiency

It is impossible for any device to operate in a cycle and Efficiency is a concept used to describe the effec-

produce work while exchanging heat only with bodies tiveness of energy conversion devices that operate in at a single fixed temperature. cycles as well as in individual system components that operate in processes. Thermodynamic efficiency, n, and The other statement is called the Clausius statement. coefficient of performance, COP, are used for devices The implications of the second law are many. For that operate in cycles. The following definitions apply: example, it allows us to (1) determine the maximum W q possible efficiency of a heat engine, (2) determine the n = q"6 COp = w maximum coefficient of performance for a refrigerator, (3) determine the feasibility of a proposed process, where Ql and Qh represent heat transferred from cold (4) predict the direction of a chemical or other type of and hot regions, respectively, Wnet is useful work pro-